Primary monohydric alcohols having 8 to 10 carbon atoms, esterified with phthalic acid, are used to a great extent as plasticizers, in particular for polyvinyl chloride. Alcohols having shorter carbon chains give plasticizers having a good gelling power, but their higher volatility is a disadvantage. Phthalic esters of longer-chain alcohols lead to plasticizers which gel slowly and have poorer cold stability.
The properties of the phthalic ester plasticizers are determined not only by the length, but also by the branching, of the carbon chain in the alcohol molecule. Alcohols having a low degree of branching give ester plasticizers which are highly prized because of their high cold flexibility. Substantially linear alcohols having 8 to 10 carbon atoms in the molecule are therefore gaining increasing importance as the alcohol component. A precondition for their use is that they be inexpensive and available in large quantities. Currently, 2-ethylhexanol is the most important alcohol component for phthalic esters; however, attempts are being made to find further raw material bases for the preparation of alcohols having the desired properties.
According to DE-C-2,855,421, phthalates of nine carbon alcohols, used as plasticizers, are obtained by oxo-reaction of eight carbon olefins, hydrogenation of the reaction product, and esterification of the resultant alcohols with phthalic anhydride. There are certain requirements of the starting olefins. They should comprise 3% to 20% by weight of compounds having an isobutane skeleton, and less than 3% by weight of compounds having a quaternary carbon atom. More than 90% by weight of the total amount of the olefins should be present as n-octenes, monomethylheptenes, and dimethylhexenes. Finally, the weight ratio of the total amount of n-octenes and monomethylheptenes to dimethylhexenes should be greater than 0.8.
Phthalic esters of ten carbon alcohols are the subject matter of European Patent Application 03 66 089. The alcohols are used in the form of a mixture which is obtained by hydroformylation of a butene fraction, aldol condensation of the resulting aldehyde mixture, and subsequent hydrogenation.
Another way to obtain didecyl phthalate mixtures is described in European Patent Application 04 24 767. The esters are prepared by a multi-stage process comprising dimerization of butene mixtures, hydroformylation and hydrogenation of the resulting octene mixture to give a nonanol mixture, dehydration of the nonanol mixture to form a nonene mixture, and hydroformylation and hydrogenation of the nonene mixture to a mixture of decanols.
The known processes still do not fulfill all the economic and technical requirements of such a process to be carried out on an industrial scale, because the starting materials are not available in sufficient quantity, are not available at a reasonable price, and/or the conversion of the starting material into the alcohols is too complex.